Known methods of determining mechanical properties of solids are based on experimental relationships of mechanical properties versus hardness of materials. A hard alloy member in the form of a sphere or cone is caused to penetrate the surface of an object being studied to produce an impression. Hardness of materials is determined as the ratio of a force pressing the indentor to the area of the impression or depth of penetration of the indentor into the surface of material. Using experimental formulae for calculations, standard mechanical properties such as ultimate strength and yield limit are determined from the hardness value. If the configuration of the impression is determined using optical test equipment after the load has been relieved from the surface of material, accuracy of hardness measurement is low since after the load removal from the surface of the material the configuration of the impression changes so as to lower accuracy of hardness measurement.
With an automatic measurement of the depth of penetration of the indentor into the surface of material during penetration of the indentor under a preset load it is not possible to record a complicated mode of material deformation, i.e. the relationship of the load at the indentor versus the depth of penetration of the indentor into the surface of material and penetration time. This method does not allow delicate processes of deformation in the indent to be studied thus substantially reducing informativity of the method.
Widely known in the art is an automatic durometer (see, e.g. U.S.S.R. publication 170721), comprising a dynamometric gauge having a first branch having a composite rod consisting of a pair of vertical movable parts mounted for movement along guides of an inner movable cylinder. The inner movable cylinder is mounted for movement along guides of a fixed outer cylinder, the inner cylinder being biased by a spring with respect to the outer cylinder. A stop washer is biased by a spring to the end of the inner movable cylinder and encloses an indentor which is secured to the lower vertical part of the composite rod. Displacement of the indentor with respect to the stop washer is measured by means of a dial gauge mounted on the fixed outer cylinder and engageable with the lower vertical part of the composite rod. The apparatus also comprises a casing accommodating an indentor loading means having a spindle secured to the second branch of the dynamometric gauge and a drive for moving the spindle.
The main load of the indentor is recorded by means of an electric contact pick-up mounted on the second branch of the dynamometric gauge and cooperating with the first branch of the dynamometric gauge.
The preload is recorded by means of an electric contact pick-up provided between the first branch of the dynamometric gauge and the spindle of the drive for moving the spindle cooperating with the second branch of the dynamometric gauge.
The prior art apparatus functions automatically and allows hardness of materials to be measured with a high enough accuracy, but it cannot ensure continuous recording of load and depth of penetration of the indentor into the surface of material so as to result in a low accuracy of measurement of hardness of materials. The use of the apparatus for objects located in radioactive zones is difficult because deactivation and maintenance of the apparatus are complicated owing to the complicated structure and presence of cavities. Rapid assembly and disassembly as well as setup of the apparatus under radiation conditions are associated with high radiation exposure of operating personnel. The provision of the two coaxially mounted cylinders and composite rod of the indentor cooperating along parallel lines of guides with appropriate free fits lowers accuracy of measurement of hardness of materials especially in various positions of the apparatus in space where it is necessary to measure hardness of vertical or inclined surfaces of various parts. The apparatus does not allow delicate processes of deformation of materials to be studied.
Widely known in the art is a portable device for measuring Brinell hardness of materials (Yu. A. Mayorov, F. M. Nikitin, Instruments for Hardness Measurements (in Russian), 1982, Mashinostroenie Publishing House, Moscow. pp. 17-19; 54-55), comprising an indentor to be pressed into the surface of material and a rod in the form of a center plate having a shank at one end thereof and the indentor rigidly secured to the other end thereof. A dynamometric gauge is mounted perpendicularly with respect to the surface of material, one branch of the gauge having a hole in which the rod shank is received. The device also comprises a means for loading the indentor having a spindle mechanically coupled to a drive for its movement and mounted coaxially with the rod on the other branch of the dynamometric gauge. The means for loading the indentor is mounted in a casing. The rod shank is engageable with a means for measuring the load of the indentor or a dial gauge mounted on the casing.
The device also comprises a means for attaching the device to an object for measurements and an optical means for measuring the diameter of impression in the material, e.g. a microscope. This device allows the final result of deformation of the surface of material such as impression or indent to be recorded so that it features a low informativity as regards processes of elastic and plastic deformation of material in the indent and a low accuracy. The device cannot be used for objects located in zones with high radiation as it cannot function automatically and calls for a permanent attendance of personnel so as to result in an increase in radiation exposure of the personnel.